Bisaminoalkyl disulfides as sensitizers and stabilizers for silver halide emulsions

ABSTRACT

The present invention relates to a process for increasing the sensitivity of photographic silver halide emulsions together with reduced fogging by the addition of bis-aminoalkyl disulfides.

United States Patent Huckstadt et al.

[151 3,647,469 5] Mar. 7, 1972 [54] BISAMINOALKYL DISULFIDES AS SENSITIZERS AND STABILIZERS FOR SILVER HALIDE EMULSIONS [72] Inventors: Harald Huckstadt, Cologne; Wilhelm Saleck, Sehildgen-Berg/Gladbach; August Randolph; Franz Moll, both of Leverl5usen, all of Qermany I [73] Assignee: Agfa-Gevaert Aktiengesellschalt, Leverkusen,Germany [22] Filed: Dec.19,l969

[211 Appl. No.: 886,747

[30] Foreign Application Priority Data Dec. 23, 1968 Germany ..P l8 16 571.4

[52] US. Cl. 36/107, 96/109 [51] lnt.Cl. ..G03c 1/28, G03c 1/34 2,438,716 3/1948 Mueller et al ..96/ 109 Primary Examiner-Norman G. Torchin Assistant Examiner-Richard E. Fichter Attorney-Connolly and But:

[57] ABSTRACT The present invention relates to a process for increasing the sensitivity of photographic silver halide emulsions together with reduced fogging by the addition of bis-aminoalkyl disulfides.

3 Claims, No Drawing BISAMINOALKYL DISULFIDES AS SENSITIZERS AND STABILIZERS FOR SILVER HALIDE EMULSIONS The sensitivity of a photographic emulsion can be affected in two ways. First, the sensitivity can be increased during the preparation of the emulsion, at the stage of so-called chemical ripening by increasing the ripening time or by adding suitable substances such as thiosulfate or other compounds which usually contain sulfur. The other method of increasing the sensitivity of a photographic emulsion consists of adding so-called development accelerators or chemical sensitizers. These are usually added to the ripened emulsion.

The compounds which have been described as development accelerators include, e.g., compounds which have an onium structure (such as quaternary ammonium and phosphonium salts and ternary sulfonium salts) and also polyalkylene oxides and polyalkylene oxide derivatives are very often employed.

Nearly all these ingredients, however, have the unfavorable side effect of increasing the fogging of the emulsion. In order to counteract this increase in fogging, which may occur not only in the heating cupboard but also in the fresh sample, it is usually necessary to increase the quantity of stabilizer. However, most stabilizers have a characteristic such that when used in substantial quantities they reduce the sensitivity. The effect of the development accelerator may thereby be impaired.

There is, therefore, an urgent need to find development accelerators or ripening agents which will not cause any increase in fogging and there is a similar need to find stabilizers which will not reduce the sensitivity of the photographic emulsion. It is desirable to find substances which would both increase the sensitivity of the photographic emulsion and which would stabilize the fogging.

This is the object of the present invention.

It has now been found that silver halide emulsions having increased sensitivity and reduced fogging are obtained by adding to these emulsions bis-aminoalkyl-disulfides or their acid salts, of the general formula:

H N(CH ),,SS(CH ),,NH,-2HX in which n may be 2 or 3, and X represents the anion of any photographically inert acid, e.g., halide, p-toluene-sulfonate, and perchlorate. The compound in which n=2 is known under the name of cystamine. The preparation of these compounds has been described in the chemical literature.

The compounds according to the invention show their advantageous effect particularly when they replace thiosulfate or other sulfur compounds in the chemical ripening. In addition to the increase in sensitivity mentioned in the examples, the considerable reduction in the fogging in the samples is very striking. This reduction in fogging can be observed not only in fresh samples but also after the samples have been stored in the heating cupboard.

The real advantage of using compounds according to the invention lies not so much in the increase in sensitivity itself, but in the combination of increase in sensitivity together with reduction in fogging, which makes it possible to add other ingredients to the emulsion, which might possibly have the effect of increasing the fogging, without a net increase in fogging resulting.

Emulsions prepared with the compounds according to the invention will, therefore, be particularly suitable for use in combination with other development accelerators. The reduced fogging will also be very important in the preparation of color emulsions since these are normally very susceptible to fogging.

The cause of the described effect of bis-aminoalkyl disulfides is still not clear. It is known that in the presence of heavy metals, particularly silver, disulfides decompose into numerous decomposition products, including mercaptans.

In U.S. Pat. No. 2,521,926, the use of bis-(ydiethylaminopropyl) disulfide as a ripening agent is described. Only this disulfide compound is described in the said patent, and it is stated there that its ripening effect is different from that of ordinary sulfur ripening agents. In the following examples, we have included the hydrochloride of this compound for comparison.

It will be seen from the examples that the effect produced according to the invention is confined to bis-aminoalkyl-disulfides, and it is not achieved in the case of the comparison compound of the U.S. patent, which is alkylated on the nitrogen atom. Although the last-mentioned compound has a certain sensitivity increasing effect, the fogging reducing effect is absent.

The compounds according to the invention may be added to the photographic emulsion at any stage of its preparation, i.e., before, during or after chemical ripening. They may also be added to the casting solution immediately before casting. The quantity added depends on the required effect and can be determined by those skilled in the art at any time by the usual tests.

It is usually sufficient to add quantities of 0.003 to 20 g. per mol of silver halide for chemical ripening. Concentrations of between 0.003 and 0.6 g. per mol of silver halide are preferred. If the compounds according to the invention are added to the casting solution of the finished emulsion, the quantities required are generally slightly higher. They are then between 0.005 and 20 g., preferably between 0.03 and 6 g. per mol of silver halide.

The compounds according to the invention may be used in any silver halide emulsions. Suitable silver halides are silver chloride, and silver bromide or mixtures thereof, if desired with a small silver iodide content of up to 10 mols percent. The silver halides may be dispersed in the usual hydrophilic compounds, for example in carboxymethylcellulose, polyvinyl alcohol, polyvinylpyrrolidone, alginic acid and its salts, esters or amides and preferably gelatin.

The emulsions also may contain other chemical sensitizers, e.g., quaternary ammonium and phosphonium salts and temary sulfonium salts, reducing agents such as stannous salts, polyamines such as diethylene triamine or sulfur compounds such as described in U.S. Pat No. 1,574,944. The above mentioned emulsions may also contain salts of noble metals such as ruthenium, rhodium, palladium, iridium, platinum or gold for chemical sensitization, as described in the article by R. Koslowsky, z. Wiss. Phot. 46, 6572 1951).

The emulsions also may be optically sensitized, e.g., with the usual polymethine dyes such as merocyanines basic or acid carbocyanines, rhodacyanines, hemicyanines, styryl dyes, and oxonols. Sensitizers of this type are described in the book by F. M. Hamer The Cyanine Dyes and related Compounds 1964 The emulsions may contain the usual stabilizers, e.g., homopolar or salt-type compounds of mercury with aromatic or heterocyclic rings (for example mercaptotn'azoles), simple mercury salts sulfonium mercury double salts and other mercury compounds. Azaindenes, especially tetra or penta-azaindenes, and in particular those which are substituted with hydroxyl or amino groups, are also suitable as stabilizers. Compounds of this type are described in the article by Birr. Z. Wiss. Phot. 47. 2 58 (1952). Other suitable stabilizers include heterocyclic mercapto compounds, e.g., phenylmercaptotetrazole, quaternary benzothiazole derivatives, and benzotriazole. The emulsions may be hardened in the usual manner, for example with formaldehyde or halosubstituted aldehydes which contain a carboxyl group, such as mucobromic acid, diketones, methanesulfonic acid esters, and dialdehydes.

The emulsions treated with bis-amino-alkyldisulfides according to the invention may also contain color couplers for the production of color photographic images.

EXAMPLE 1 A silver iodobromide emulsion containing 5 mols percent of silver iodide is prepared in the usual manner. The pAg is adjusted to 8.9 the pH to 6.8 and the viscosity to 8 cp. for after ripening. Gold thiocyanate is then added and the emulsions is divided into four equal parts. The following additions are then made to the individual samples (based on 1 kg. of emulsion) containing g. of silver bromide with a silver iodide content of 4 mols percent:

Sample A: Comparison samplewithout additive Sample B: 3.3 mg. of a compound of the following formula Sample D: 3.3 mg. of a compound of the following formula (for comparison) CzHs acetate, exposed in the sensitometer behind a grey step wedge and developed at 20 C. in a developer of the following composition:

Sodium sulfite sicc. 70.0 g. Na B.O lH,0 7.0 g. Hydroquinone 3.5 g. p-monomethyl aminophenol 3.5 g. Sodium citrate 7.0 g. Potassium bromide 0.4 g.

. made up to 1 liter with water.

The development time is 6 minutes.

TABLE 1 Sample Sensitivity y fog fog (3 days 60' C.)

A Comparison sample 0.84 0.16 0.21 B +2.0 0.87 0.1 1 0. I C +1.8 0.86 0.12 0.15 D +1.0 0.88 0.16 0.2]

A difference of 3 corresponds to a sensitivity difference of oneshutter stop.

lclaim:

l. A light sensitive photographic material having at least one silver halide emulsion layer, which contains a sensitizing amount of a compound of the following general formula:

wherein X is the anion of any photographically inert acid.

2. A light sensitive, photographic material according to claim 1, wherein, the emulsion layer in addition contains color couplers.

3. In the process for the preparation of photographic'silver halide emulsions by the precipitation of the'silver halide in the presence of the protective colloid, and washing and chemical ripening the improvement according to which the chemical ripening is carried out in the presence of an effective amount of a compound of thefollowing formula:

z)n z' H wherein X the anion of any photographically inert acid. 

2. A light sensitive photographic material according to claim 1, wherein the emulsion layer in addition contains color couplers.
 3. In the process for the preparation of photographic silver halide emulsions by the precipitation of the silver halide in the presence of the protective colloid, and washing and chemical ripening the improvement according to which the chemical ripening is carried out in the presence of an effective amount of a compound of the following formula: H2N-(CH2)n-S-S-(CH2)n-NH2.2HX wherein n 2 or 3; X the anion of any photographically inert acid. 